Summary of work: In general, the experimental Hematology Section is investigating a) the structure, function, and molecular biology of the hFRs, b) the role of hFRs in the transport of folates and antifolates and the mechanism whereby hFRs internalize ligand, and c) the regulation of hFR expression. We have previously shown that human folate receptors (hFR), are constituents of gene family of ubiquitously expressed glycoprotein isoforms named hFR-KB (alpha hFR), HFR-P (beta hFR), and tau HFR. The KB cell isoform is the best characterized receptor and mediates folate and antifolate transport. Our recent studies have demonstrated that expression of the hFRs is an important determinant of antifolate mediated cytotoxicity and of acquired drug resistance, and permits cellular proliferation of non-expressing cells under folate limiting conditions. The factors regulating expression of each isoform in a tissue specific manner, the mechanism(s) whereby the receptor mediates ligand internalization, and the structural/function domains of the proteins are unknown. In the past year, we have published data describing the structural and functional analysis of the P4 promoter of the hFR-KB gene, the role of conserved tryptophan residues in the structure and function of the hFR, and the effect of cotranslationaly addition of a GPI anchor on the sorting and processing of the KB hFR isoform. We have submitted manuscripts describing the structural components of the KB cell hFR gene, and the relationship between caveolin and the hFR relative to sorting and function. In preliminary work, we are investigating the structure and function of the Pi promoter of the hFR gene; the regulation of expression of each of the hFR isoforms; the structure and expression of the tau hFR gene; the effect of hFR antisense constructs on cellular proliferation; the role of glycosylation of the hFR on the functional properties of the protein; the role of folates (and antifolates) on neural tube defects in Xenopus laevis embryos; and characterization of a leukemia cell line obtained from a patient with therapy related acute myeloid leukemia.